By Alex Chamwada NAIROBI, Kenya Apr 28 - They look like fish ponds. But no. They are sewer ponds used for biological treatment of sewage from the city of Nairobi. The ponds are part of the tail end of the treatment process as it all begins with the separation of debris from the liquid waste. The plant is located in Ruai, some 30 Kilometres from the city but it has retained its original name - Dandora Estate Sewage Treatment Works since its establishment.